1. Field of the Invention
The present invention generally relates to a projector having heat-generating elements such as polarizing plates and liquid crystal panels, and particularly relates to a projector provided with cooling mechanisms for cooling the heat-generating elements.
A projector, such as a liquid crystal projector, is provided with an optical system including elements such as a folding mirror, color separating dichroic mirrors, liquid crystal panels, color composition mirrors (prism). Since the liquid crystal panels and polarizing plates provided adjacent to the liquid crystal panels absorb light and generate heat, it is necessary to cool the liquid crystal panels and the polarizing plates. Therefore, there is a need for efficiently cooling the liquid crystal panels and the polarizing plates.
Also, the projector is commonly used for meetings and presentations in an office or may be used as a home image output device (a screen for television and games). Therefore, there is a need for reducing the noise generated by the projector.
Further, since the projector is provided with a fine optical system as described above, in order to improve the quality of the projected image and to improve the reliability of the projector itself, it is necessary to prevent dust from entering the projector.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a projector 10 of the related art will be described to facilitate the understanding of the projector of the present invention. FIG. 1 is a transverse cross section of the projector 10 and FIG. 2 is an enlarged diagram showing a portion of the projector of the related art provided with air intake fans 29 to 31.
As shown in FIG. 1, the projector 10 includes an inner housing 11, an outer housing 12, a light source 13, liquid crystal panel units 24 to 26, a projecting lens 27, the air intake fans 29 to 31 and an air discharge fan 32.
The inner housing 11 is provided inside the outer housing 12, and a space 28 is formed between the inner housing 11 and the outer housing 12. The inner housing 11 surrounds an optical system including elements such as total reflection mirrors 14 to 16, color separation dichroic mirrors 17 and 18, color composition dichroic mirrors 19 and 20, condenser lens 21 to 23, and the liquid crystal panel units 24 to 26.
The projector 10 having the above-described optical system generates images in the following manner. When passing through the optical system, light emitted from the light source 13 is separated into beams of, for example, three fundamental colors by means of the color separation dichroic mirrors 17 and 18. Then, the separated beams are directed through the liquid crystal panel units 24 to 26 so as to be subjected to an image signal superimposing process for each color. This image signal superimposing process may also be referred to as an image modulation process.
Then, the beams are color composited through the color composition dichroic mirrors 19 and 20. The beams are then projected through the projecting lens 27 towards a screen (not shown).
The above-described liquid crystal panel units 24 to 26 each includes a liquid crystal panel and a pair of polarizing plates provided on either sides of the liquid crystal panel. The liquid crystal panel and the polarizing plates absorb light and generate heat. Since polarizing film made of organic material is normally used as the polarizing plates, the liquid crystal panel units 24 to 26 will be degraded when heated to a temperature exceeding 70xc2x0 C.
In order to prevent the liquid crystal panel units 24 to 26 from being overheated, the air intake fans 29 to 31 are provided on a lower surface of the inner housing 11 at a position opposing the liquid crystal panel units 24 to 26. The air intake fans 29 to 31 generate cooling airflows which are directed to polarizing plates of the liquid crystal panel units 24 to 26. Thus, each of the polarizing plates is air-cooled.
The temperature of the cooling airflows is raised when passing by the polarizing plates of the liquid crystal panel units 24 to 26. Thus-heated airflows are discharged into the outer housing 12 through vents 33, 34, 35 provided in a top plate of the inner housing 11. Further, the heated airflows are discharged outside the apparatus through external vent 36 by means of the discharge fan 32.
The space 28 also includes various devices 39a other than the inner housing 11. There are some devices 39a which may generate heat. The light source 13 also generates heat. In order to cool the heat-generating devices 39a and the light source 13, the projector 10 is provided with internal cooling fans 39 for each of the devices 39a and the light source 13.
In the FIG. 2, three air intake fans 29 to 31 are provided to correspond to the number of liquid crystal panel units 24 to 26 provided in the projector 10. However, as illustrated in FIG. 3, the liquid crystal panel units 24 to 26 may be cooled by a single air intake fan 37 via an air-conducting duct 38.
Thus, the degradation of the polarizing plates and the liquid crystal panels due to heat can be prevented by means of the air intake fans 29 to 31 provided at positions opposing the liquid crystal panel units 24 to 26. Thus, the reliability of the projector 10 is improved.
However, since each of the air intake fans 29 to 31 generates cooling airflows by rotating its blades, there is a drawback that whistling sounds are generated when the blades of the fans cut through the air. These whistling sounds give rise to a noise during operation of the projector 10. With the structure illustrated in FIG. 2, since each fan 29 to 31 generates whistling sounds, the noise is increased. With the structure illustrate in FIG. 3, although there is only one air intake fan 37, the noise is increased since the air-conducting plates cut through the air flowing within the air-conducting duct 38.
Thus generated noise passes through the inner housing 11 and is transferred to the space 28 between the inner housing 11 and the outer housing 12 via the vents 33 to 35 formed in the inner housing 11. Then, the noise is reflected of f the walls of the outer housing 12 and is transferred to the external vent 36. Finally, the noise propagates outside the projector 10 through the external vent 36.
FIG. 4 is a diagram showing a chart of noise values generated in the projector 10 of the related art. The chart includes columns indicating name, number, type, applied voltage, and noise value of each fan provided in the projector 10. The noise value represents a value measured using a measuring device provided at the external vent 36.
As can be seen from FIG. 4, when only three air intake fans 29 to 31 were driven, the noise value was 40.0 dB. When only the air discharge fan 32 was driven, the noise value was 41.8 dB. When only three internal cooling fans 39 were driven, the noise value was 39.5 dB.
Also, when all the fans, that is to say, the air intake fans 29 to 31, the air discharge fan 32 and the internal cooling fans 39 were driven, the noise value amounted to 46.1 dB. Accordingly, the projector 10 of the related art has a drawback that a large noise is produced.
Accordingly, it is a general object of the present invention to provide a projector which can obviate the drawbacks described above.
It is another and more specific object of the present invention to provide a projector which can positively implement the cooling process while reducing the noise propagating out therefrom.
In order to achieve the above objects according to the present invention, a projector includes:
a first housing provided with first heat-generating elements used for generating an image, first fans producing cooling airflows towards each one of the first heat-generating elements and vents via which the cooling airflows heated by the first heat-generating elements are discharged;
a second housing in which the first housing is installed, the second housing being provided with second fans discharging the cooling airflows outside the projector; and
a sound insulating member provided on a path between the vents and the second fans so as to insulate sounds produced by the first fans.
With the projector described above, a noise is prevented from propagating outside the projector through openings provided with the second fans.